This invention relates generally to enhancement of the combined grade of service (GOS) and quality of service (QOS) in a wireless telecommunications system and, more particularly, to adjustment of one or more forward link transmission power limitation thresholds in relation to measured traffic demands on a wireless forward link.
In code division multiple access (CDMA) wireless telecommunications and similar xe2x80x9cspread spectrumxe2x80x9d transmission systems, transmissions are made within one or more ranges of frequencies, such as F1, F2, F3 through Fn, also referred to as xe2x80x9ccarriers.xe2x80x9d In simplistic terms, individual calls within each carrier are separated and differentiated from each other by codes transmitted and detected by the respective transmission and receiving equipment handling the calls. In a mobile wireless system, such equipment is provided in the form of one or more mobile handset transceivers (MSs) and a base station transceiver (BTS) that is capable of handling calls to multiple MSs simultaneously. Transmissions from each BTS to each MS is conducted through a wireless xe2x80x9cforward link,xe2x80x9d while transmissions from each MS to each BTS is conducted through a wireless xe2x80x9creverse link,xe2x80x9d In general, each call between a BTS and an associated MS thus includes a forward and a reverse link.
The traffic capacity or grade of service (GOS) and quality of service (QOS) available over each frequency band or carrier (e.g. F1, F2, F3, through Fn) provided by each BTS in a CDMA or other spread spectrum system is limited. Grade of service generally refers primarily to the probability of new calls to or from the BTS being blocked, while quality of service generally refers primarily to the fidelity or integrity of sound or data transmissions.
In CDMA systems, capacity or GOS limitations are primarily imposed by forward link power transmission constraints which limit the total power available for new calls, handoffs and hand-overs over the forward link of each carrier below a maximum high power amplifier (HPA) limit of the BTS. Moreover, limitations and the QOS of the total forward link are also imposed by interference between all calls within the carrier, which increases as the total transmission power over the carrier increases to accommodate new calls, handoffs and hand-overs. Because each new call, hand-over and handoff uses an additional amount of power and capacity over the forward link of a carrier, an allocation is made of the total available power for new calls on one hand, and hand-overs and handoffs on the other hand, to provide the desired combination of GOS and QOS.
There are two thresholds for forward link power allocation to new call attempts and soft handoff attempts. Call blocking threshold is the first digital threshold as the digital power sum increases in normal operation. When the digital power sum for all channel elements of a sector is above this threshold, the BTS blocks all new call attempts for the sector. However, handoffs into the sector are still allowed to maintain existing calls. Handoff blocking threshold is the second digital threshold to be reached. If it is exceeded, the BTS blocks all further handoffs into the sector.
Both parameters are currently set empirically or, in other words, based on general experience in the field. Usually, the handoff blocking threshold is set higher than the call blocking threshold, giving handoff attempts a higher priority than new call attempts. This gives a higher priority to avoiding denial of handoff attempts, which would result in dropped calls. A lower priority is given avoiding denial of new call attempts because only a busy signal would result.
It is a common practice to empirically set the handoff blocking threshold high enough such that handoff blocking is a rare event. Moreover, it is observed that variation of the handoff blocking threshold, after it is set higher than a certain value, has negligible impact on blocked handoffs. Thus, it is preferable that the call blocking threshold is set to balance the GOS and QOS. If the call blocking threshold is set too low, the call blocking probability will be unacceptably high, because there will be too little power available for new call attempts. If the threshold is set too high, an unacceptably high probability that the actual output power will reach the maximum amount of analog transmit power allowed at the output of the HPA will result, which could cause power limiting of the sector. During power limiting, the total HPA output power is forced below its limit. Because of this sudden overall power decease, every user is punished equally with same amount of reduced power. This may cause high FER for users in the sector, call dropping and reduction of both QOS and GOS.
Currently, there is no systematic method of setting the call blocking threshold. The call blocking threshold is set empirically as a fixed value regardless of the traffic and mobility condition in a sector. The fixed threshold can not accommodate well geographic areas in which traffic and mobility demand at the busy hour (e.g., highways) and during regularly scheduled events (e.g., stadiums) swells dramatically and thus may cause either a high call blocking rate or a high probability of power limiting. The limitation of this current method of forward link power allocation unnecessarily limits the capacity and GOS of CDMA system.
In the past, the well-known Erlang-B formula has been used for estimating forward link capacity and call blocking probability in CDMA system. However, the Erlang-B formula was developed for wireline systems. It is not as predictable of CDMA system performance, since it does not take into account the variable nature of the CDMA RF environment, mobility in cellular systems, and assignment of a higher priority to handoff attempts than admission of new call attempts. The limitation of this current traffic provisioning method results in inaccuracy of CDMA system traffic and performance measurement.
It is an object of the present invention to provide a method to replace the conventional method for setting the call blocking threshold and to provide a method to replace the Erlang-B formula for traffic provisioning in CDMA systems.
These and other limitations associated with current CDMA management and control systems are overcome by the present invention, in which the new call blocking threshold of one or more BTS forward links is adjusted to compensate for variation in traffic and mobility demand, which results from new call attempts, handoff attempts, and the like. In one aspect of the invention, there is provided a method of determining call blocking probability and power limiting probability for given traffic and mobility demands and a given call blocking threshold. In yet another aspect of the invention, there is provided a method of adjusting the call blocking threshold in relation to anticipated traffic and mobility demands. In yet another aspect of the invention, anticipated traffic demand from new calls and user mobility are derived from operational measurement data obtained and stored in a management and control system. In still another aspect of the invention, the new call blocking threshold is adjusted with a frequency relating to the rate of change in traffic and mobility demand.